Electromagnetic styluses are known in the art for use and control of a digitizer. Position detection of the stylus provides input to a computing device associated with the digitizer and is interpreted as user commands. Position detection is performed while the stylus tip is either touching and/or hovering over a detection surface of the digitizer. Often, the digitizer is integrated with a display screen and a position of the stylus over the screen is correlated with virtual information portrayed on the screen.
PCT Patent Publication No. WO2008086058 entitled “Multiple Styli Annotation System,” the contents of which is incorporated herein by reference, describes an apparatus for stroke capture and retrieval that works with an annotation capture and recording system that can operate with several styli active at the same time. The apparatus includes at least one ultrasound signal sensor operative to receive ultrasound signals from one or more styli when the one or more styli are operating in a defined working area of the apparatus and at least one electromagnetic receiving unit operative to receive electromagnetic signals from an electromagnetic transmitter of the stylus. Coordination between the apparatus and a plurality of styli is provided by a controller that instructs each of the styli to transmit its ultrasound signal at a dedicated time slot. Positioning is determined and tracked based on received ultrasound signals.
U.S. Pat. No. 7,292,229 entitled “Transparent Digitizer” which is assigned to N-trig Ltd., the contents of which is incorporated herein by reference, describes a passive electro-magnetic stylus which is triggered to oscillate at a resonant frequency by an excitation coil surrounding a digitizer. The oscillating signal is sensed by the digitizer. The stylus operates in a number of different states including hovering, tip touching, right click mouse emulation, and erasing. The various states are identified by altering the resonant frequency of the stylus so that the stylus resonates at a different frequency in each state. A position of the stylus, e.g. a position of the stylus' tip with respect to the digitizer sensor is determined based on signals sensed from sensor.
U.S. Patent Application Publication No. 2008/0128180 entitled “Position Detecting System and Apparatuses and Methods for Use and Control Thereof” assigned to N-Trig Ltd., the contents of which is incorporated herein by reference, describes an electromagnetic stylus that emits signals at an oscillation frequency that can be picked up by a digitizer sensor and used to determine its position on the sensor. The stylus includes a variable element, e.g. a resistor, capacitor, or an inductor, that is responsive to pressure exerted on the stylus tip by the user and triggers changes in the frequency emitted by the stylus. The digitizer system is operable to discern between different frequencies emitted by the stylus to determine a position of the stylus and a pressure exerted on the stylus tip by the user.
U.S. Patent Application Publication No. 2008/0238885 entitled “System and method for multiple object detection on a digitizer system” assigned to N-Trig LTD, the contents of which is hereby incorporated by reference, describes a digitizer system including at least one object with an electronic tag configured for radiating at least one modulated signal and at least one second signal; a digitizer sensor configured for detecting the at least one second signal while the object is positioned on or over the digitizer sensor; and circuitry configured for identifying the object based on modulation of the at least one modulated signal and for determining a position of the object on or over the digitizer based on the detected second signal on a portion of the digitizer sensor. Optionally, the modulated signal is transmitted in response to an excitation signal.
U.S. Pat. No. 5,571,997 entitled “Pressure sensitive pointing device for transmitting signals to a tablet” the contents of which is incorporated herein by reference, describes a pressure sensitive pointing device or pen for use with an electronic tablet that determines the position of the pointing device on the surface of the tablet. The pointing device incorporates a variable reluctance circuit responsive to the force exerted on the pen point for modulating a radiating frequency, emanating from the pen, in proportion to the force.